107 



In 1844 Unger furnished a long and most explicit account of this fungus DR. M. C. 

 which had proved so destructive to the carp in the tanks of the Botanic COOKE. 



Gardens at Gratz. He described the appearance of the fish, their movements, 



the effects of the parasite, and finally gave a full description, with excellent 

 figures of the fungus itself.* From this account it is clear that there was no 

 other disease, but that the fish were being destroyed by the parasite. The 

 quotation of his entire paper would only be to rewrite what has already been 

 written of the salmon disease. 



In 1851 M. Davaine exhibited at a meeting of the Societe de Biologie a carp 

 suffering from the attacks of this disease, and the subject came under discus- 

 sion, the gist of which was afterwards published in the Comptes rendus. Thus, 

 coming down to our own times we have records of the same form of disease 

 attacking fish, especially the head and tail, and the same fungus present upon 

 the diseased spots. t The fungus of the salmon disease is precisely identical 

 with that of the carp, the ova of fishes, and that also which is found on the 

 pike and other fresh-water fishes, including sticklebacks. 



Some years ago, when aquaria were the fashion, I had an aquarium. It was 

 a large bell glass, reversed, capable of containing about a pail of water, and in 

 it were three carp. The water was seldom changed or aerated, and one day I 

 discovered the head of one of the fish quite fiocculent with the disease. At once 

 I determined upon giving the fish a tonic. They were evidently much debili- 

 tated. Therefore I placed the aquarium under the water-tap of the cistern, and 

 allowed the water to run in in a continuous stream, the overflow passing down 

 the " sink." Day and night for a week this constant flow of fresh water was 

 continued. The fish became quite lively, and the operation was afterwards 

 repeated daily, for about an hour every day. The diseased carp wholly recovered, 

 all signs of fungus disappeared, and I had them for a twelvemonth afterwards, 

 until the glass was accidentally broken, and never replaced. This incident is 

 quoted to show the influence of well aerated water in recovering the healthy 

 tone of the fish, and enabling them to overcome the attacks of the disease. It 

 seems to show that an invigorated constitution is antagonistic to the parasite. 



Secondary Causes. — These may be of such a nature as to influence very 

 materially the prevalence of the disease. There is no probability of its being 

 wholly eradicated, but it may be mitigated, and this more by attention to the 

 secondary causes than by any process of destroying the fungus itself. One 

 of the evident helps, or secondary causes, of the disease are wounds or bruises on 

 the naked parts of the fish. These may originate by fighting together for mates, 

 or in unsuccessful attempts to overcome obstructions in their passage up or 

 down the river, whether weirs or dams, whatever impedes their progress leads to 

 effort, and in making continued efforts, and failing, the soft parts are bruised, 

 or wounded, it may be but slightly, and yet sufficient to afford a nidus for the 

 fungus spore. It has long been known that it is the bruised ova which are 

 first attacked, even so slightly as may be caused by a touch or beating against 

 the side of the vessel which contains them. So it is with fish in aquaria ; if 

 they are handled they are predisposed to attack, unless in robust health. If 

 salmon are in robust health even a slight bruise would not result in parasitism, 

 but it is evident that their constitution has not been so good as formerly, 

 because the disease has been in existence half a century, and only recently so 

 fatal in effects, which points to a second accessory cause, namely, that of con- 

 stitutional debility. All the evidence goes to show that it is debilitated fish 

 which are in most instances sufferers. Instances of known debility from re- 

 tention of ova, or spawning, make the bulk of fatal cases. The few which are 

 supposed to have been strong fish were, it may well be assumed, exhausted, or 

 otherwise "low." Even if they escape wounds or bruises in overcoming 

 obstacles in their way up, the efforts would produce an exhaustion favourable 

 to attack. Human experience teaches us that fatigue and exhaustion are helps 

 to the attacks of epidemic disease. It must not be forgotten that low water is 

 a source of debility to fish in general through lack of food. "What angler does 

 not know that when waters are high, succeeding plenty of rain, that food is 

 washed down from the land, and successful angling out of the question. The 



* Ann. des Sci. Nat. (Botanique), 1844, p. 1. 



f A resume of this history will be found in Kobin's Histoire Naturelle des 

 Veyetaux Parasites, (Paris, 1853), p. 382. 



